Environmental conditions could be critical for maintaining mental health including memory and its neural mechanisms. Whereas much attention has been devoted to the effects of enriched physical environment on memory and the hippocampus, the effects of social environment remain poorly investigated. Many animal species including humans are highly social and complex social interactions are an integral part of their natural environment. To understand maintenance of healthy memory and neurological consequences of social disorders, it is it crucial to investigate how social environment might influence memory and the brain. The proposed study will investigate the relationship between social environment, memory, hippocampal structure and neurogenesis using a food-caching bird, mountain chickadee, as a model. Hippocampus, which is involved in memory function, is well known for its plasticity and there is growing evidence that new neurons are generated in the hippocampus throughout adult life span. The proposed study will specifically investigate whether naturally rich social environment is required for maintaining healthy memory and the brain and whether social isolation results in impaired memory, fewer hippocampal neurons and reduced neurogenesis rates including both cell proliferation and neuron survival. Fully grown birds of the same age will be randomly assigned to five different social environments: solitary, unisex male pairs, unisex female pairs, male-female pairs and groups including two male-female pairs. Adult humans and chickadees naturally exist in large groups consisting of male-female pairs - thus the last experimental group will represent the most natural social environment. All birds will be maintained in cages providing equal space per bird for all groups. All birds will be maintained in their assigned social environment for 90 days during which they will be regularly tested in various memory tasks. At the end of the experiment all birds will be sacrificed for the analyses of the hippocampus structure (volume, neuron count) and neurogenesis (using BrdU and Phospho-histone H3 Mitosis markers). This study will provide important information on the effects of social environment on memory and the hippocampus which, in turn, might help better understand consequences of social disorders for mental health and the brain.